Light emitting display apparatus

ABSTRACT

There is provided a light emitting display apparatus including at least a light emitting element and a thin film transistor (TFT) for driving the light emitting element, characterized in that a mechanism is provided in which a semiconductor constituting the TFT is irradiated with at least a part of light whose wavelength is longer than a predetermined wavelength among the light emitted by the light emitting element.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of co-pending U.S. patent applicationSer. No. 15/878,825, filed Jan. 24, 2018; which is a Continuation ofco-pending U.S. patent application Ser. No. 15/243,091, filed Aug. 22,2016, now U.S. Pat. No. 9,911,797, issued Mar. 6, 2018; which is aContinuation of co-pending U.S. patent application Ser. No. 14/842,649filed Sep. 1, 2015, now U.S. Pat. No. 9,450,037, issued Sep. 20, 2016;which is a Continuation of co-pending U.S. patent application Ser. No.14/059,949 filed Oct. 22, 2013, now U.S. Pat. No. 9,153,635 issued Oct.6, 2015; which is Continuation of co-pending U.S. patent applicationSer. No. 13/001,000, filed Dec. 22, 2010, now U.S. Pat. No. 8,592,815issued Nov. 26, 2013; which is a National Phase application ofInternational Application PCT/JP09/062263, filed Jun. 30, 2009, whichclaims the benefit of Japanese Patent Application No. 2008-174484, filedJul. 3, 2008 which is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to a light emitting display apparatusincluding a TFT.

BACKGROUND ART

For achieving high performance, low temperature manufacturing processand low cost of a thin film transistor (TFT), a wide variety of channellayer materials have been studied at present. The materials includeamorphous silicon, polycrystal silicon, microcrystal silicon and organicsemiconductor, for example.

An oxide semiconductor found in recent years is another potentialcandidate as the material. A TFT using in its channel layer an amorphousIn—Zn—O(IZO) thin film and an amorphous In—Ga—Zn—O(IGZO) thin film isdisclosed in papers: Barquinha et al., J. Non-Cryst. Sol., 352, 1756(2006); and Yabuta et al., Appl. Phys. Lett., 89, 112123 (2006).

A TFT exhibits a threshold voltage different according to asemiconductor material of its channel layer and manufacturing process.The threshold voltage of the TFT is changed by various causes (such asmanufacturing process hysteresis, aging, electrical stress and thermalstress). The electrical stress is caused by applying voltage or currentto a semiconductor. The thermal stress is caused by external heating orJoule heat generated by applying current to a semiconductor. Actually,these stresses are sometimes simultaneously applied to the TFT.

The threshold voltage of the above oxide semiconductor TFT isunexceptionally changed by the electrical stress or a composite of theelectrical and the thermal stress. This is disclosed in papers: Riedl etal, Phys. Stat. Sol., 1, 175 (2007); and Kim et al., InternationalElectron Device meeting 2006 (IEDM'06), 11-13, 1 (2006).

There is disclosed that irradiating the oxide semiconductor TFT with avisible light and an ultraviolet ray changes various properties of theTFT including the threshold voltage in papers: Barquinha et al., J.Non-Cryst. Sol., 352, 1756 (2006); and Gorrn et al., Appl. Phys. Lett.,91, 193504 (2007). For polycrystal silicon, Japanese Patent ApplicationLaid-Open No. H10-209460 discloses a method of reducing the thresholdvoltage by irradiating the channel layer of the TFT with light.

Many experiments have been done to provide each pixel with an electricalcircuit formed of a plurality of transistors and capacitors in a lightemitting display apparatus to compensate change in the thresholdvoltage.

DISCLOSURE OF THE INVENTION

A TFT for driving a pixel used in an electroluminescence light emittingdisplay apparatus has a problem in that electrical or thermal stressapplied to the TFT caused by driving the light emitting element changesthe threshold voltage with time. This is because the electroluminescencelight emitting display apparatus causes a disturbance of an image bychange in the threshold voltage during the operation of the apparatus.

Compensating change in the threshold voltage has required forming anelectrical circuit (compensating circuit) using a large number of TFTsand capacitors for each pixel. This method, however, increases thenumber of TFTs per pixel and makes it difficult to increase theresolution of the display apparatus.

The present invention has been made in view of the above problems and anobject of the invention is to provide a light emitting display apparatuscapable of compensating or suppressing change in the threshold voltageof a driving TFT.

The present invention is directed to a light emitting display apparatusincluding at least a light emitting element and a thin film transistor(TFT) for driving the light emitting element,

characterized in that

a mechanism is provided in which a semiconductor constituting the TFT isirradiated with at least a part of light whose wavelength is longer thana predetermined wavelength among the light emitted by the light emittingelement.

The wavelength of the light with which the semiconductor constitutingthe TFT is irradiated can be longer than the absorption edge wavelengthof the semiconductor.

The light emitting display apparatus can further comprises a unit forshielding the semiconductor constituting the TFT from the light whosewavelength is shorter than the absorption edge wavelength of thesemiconductor.

The shielding unit can be a color filter.

The surface density of in-gap level of the semiconductor can be 10¹³cm⁻² eV⁻¹ or less.

The semiconductor can be an oxide semiconductor including any of In, Ga,Zn and Sn.

In the light emitting display apparatus, the TFT at least can include agate electrode formed on a substrate, an insulating film formed to coverthe gate electrode, a semiconductor formed on the insulating film and asource and a drain electrode formed on the semiconductor,

a light shielding film can be provided between the light emittingelement and the semiconductor, and

the mechanism can include a light transmissive region formed in at leasta part of the light shielding film.

The light transmissive region can be a slit.

The mechanism can be a reflector that reflects at least a part of lightwhose wavelength is longer than a predetermined wavelength among thelight emitted by the light emitting element and provided in a positionwhere the reflector can reflect the light to the semiconductor of theTFT.

In the light emitting display apparatus, the TFT can include at least asource and drain electrodes formed over a substrate, the semiconductorformed to extend over the source and drain electrodes, an insulatingfilm formed to cover the semiconductor and a gate electrode formed onthe insulating film, and

the mechanism can include a light transmissive region provided in atleast a part of the gate electrode.

The present invention can compensate or suppress temporal change in thethreshold voltage of the driving TFT or change due to electrical orthermal stress in the light emitting display apparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of the light emitting display apparatusaccording to an embodiment of the present invention.

FIG. 2 is a cross section of a TFT describing the present invention.

FIG. 3 is a chart describing the influence of light irradiation on thetransfer characteristic of the TFT to which the present invention can beapplied.

FIG. 4 is a chart describing a second example.

FIG. 5 is a cross section of the light emitting display apparatusaccording to another embodiment of the present invention.

FIG. 6 is a cross section of the light emitting display apparatusaccording to further another embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

The embodiment of the light emitting display apparatus according to thepresent invention is described in detail below with reference to thedrawings.

FIG. 1 is a cross section of the light emitting display apparatusaccording to an embodiment of the present invention. A gate electrode 20is provided on an insulating substrate 10, a gate insulating film 30 isprovided on the gate electrode 20 and the substrate 10 to cover the gateelectrode 20 and a semiconductor film 40 is provided on the gateinsulating film 30. In addition, a source electrode 50 and a drainelectrode 50 are provided on the semiconductor film 40 and a channelprotecting film 60 is provided to cover the semiconductor film 40, thesource electrode 50 and the drain electrode 51 to form a thin filmtransistor (TFT) for drive. A light shielding film 70 is provided on thechannel protecting layer 60 to cover the semiconductor film 40 whenviewed from the top. A protective film 80 is provided on the lightshielding film 70 and the channel protecting layer 60. The sourceelectrode 50 is connected to an anode electrode 90 through a contacthole 81 to constitute a light emitting element formed of a holetransport layer 100, a light emitting layer 110, an electron transportlayer 120 and a cathode electrode 130. The TFT, the light emittingelement and a desiccant 140 are sealed by a sealing cap 150 to form thelight emitting apparatus.

The light shielding film 70 is provided with a mechanism for irradiatingthe semiconductor forming the TFT with at least a part of light whosewavelength is longer than a predetermined wavelength among the lightemitted by the light emitting element. The semiconductor is irradiatedwith at least only a part of light among the light emitted by the lightemitting element, whose wavelength is longer than the predeterminedwavelength, through the mechanism. This allows suppressing or changingthe threshold voltage of the TFT changed due to aging, electrical stressand thermal stress. The reason why the threshold voltage of the TFT ischanged by irradiating the semiconductor with the light is that fixedcharge such as a carrier trapped inside the semiconductor or around thesemiconductor, for example, may be released by irradiation with light.Irradiation with light whose wavelength is shorter than the absorptionedge wavelength of the semiconductor increases S value of a transfercurve to change a curve profile and TFT properties in addition to thethreshold voltage, which requires the irradiation of the semiconductorwith the light whose wavelength is longer than the predeterminedwavelength.

In the present embodiment, there is provided in the light shielding film70 a light transmissive region 71 for transmitting at least a part ofthe light as the mechanism for irradiating the semiconductor with atleast a part of light whose wavelength is longer than the predeterminedwavelength among the light emitted by the light emitting apparatus. Ifthe light emitted by the light emitting element is longer in wavelengththan the predetermined light, it is enabled to use a slit provided inthe light shielding film 70 as the light transmissive region 71.

The transmittance of the light transmissive region 71, an areal ratio ofthe light transmissive region 71 to the light shielding film 70 and theposition thereof may be determined from the wavelength of light emittedby the light emitting layer 110 and the amount of change in thethreshold voltage of the TFT. Suppose that the threshold voltage of theTFT is comparably changed using two kinds of light emitting layers eachemitting light whose wavelength is different from each other. The areaof the light transmissive region 71 needs to be smaller, in the casewhere the light emitting layer emitting light whose wavelength is short(a center wavelength is approximately 460 nm) is used, than the casewhere the light emitting layer 110 emitting light whose wavelength islong (a center wavelength is approximately 650 nm) is used. This isbecause the short wavelength larger in energy than the long wavelengthincreases the amount of shift in the threshold voltage of the TFT,requiring the amount of light reaching the semiconductor film to bereduced by decreasing the area of the light transmissive region 71. Thetransmittance of the light transmissive region 71, an areal ratio of thelight transmissive region 71 to the light shielding film 70 and theposition thereof are determined so that the threshold voltage of the TFTcan be changed in an appropriate range by the above method.

It is desirable to adjust the wavelength to a wavelength longer than theabsorption edge wavelength of the semiconductor to irradiate the lighthaving the adjusted wavelength with the semiconductor. This allows thesemiconductor to be recovered to the state nearest to properties beforethe occurrence of change in the threshold voltage. In the presentinvention, the term absorption edge wavelength refers to a wavelengththe lowest in energy in light absorption based on interband transitionof a free carrier in the semiconductor. As used in a general amorphoussemiconductor, the absorption edge wavelength of the present inventionis defined by an x-intercept extrapolated to the x axis with √ahvplotted with respect to photon energy hv, where, h is Planck constant(J·s), v is oscillation frequency (Hz) of a photon and a is absorptioncoefficient (cm⁻¹).

It is also desirable that the semiconductor is sufficiently shieldedfrom light whose wavelength is shorter than the absorption edgewavelength. This is because irradiation with a short-wavelength lightsignificantly changes other properties in addition to the thresholdvoltage. The influence remains on the semiconductor after theshort-wavelength light is shut off as is the case with a long-wavelengthlight. The change in various properties of the semiconductor during theirradiation of the semiconductor with light whose wavelength is shorterthan the absorption edge wavelength may be associated with significantchange in carrier density of valence band and conduction band or theoccupational state of in-gap levels due to the interband transition of acarrier by light. For this reason, the light emitting display apparatuscan be further provided with a unit capable of sufficiently shieldinglight whose wavelength is shorter than the absorption edge wavelength.

A color filter may be used as the unit for sufficiently shielding light.The color filter selectively transmits only light in a requiredwavelength range and is arranged at any position of an optical paththrough light emitted from the light emitting element reaches thesemiconductor. The color filter provides transmitted light withappropriate intensity attenuation, so that the color filter is suited tobe used as a dimming mechanism for adjusting the intensity or thewavelength of irradiation light in a semiconductor device. The colorfilter is in a film form or in a plate form and suited to be arranged inthe apparatus. The color filter is generally inexpensive and can reducethe increase in cost due to the arrangement of the dimming mechanism asmuch as possible.

As another example of the mechanism for irradiating the semiconductorwith at least a part of light whose wavelength is longer than thepredetermined wavelength, a reflector may be provided on the substrateas illustrated in FIG. 5. Although a reflector 21 is provided as areflector in an example in FIG. 5, the part corresponding to thereflector may be surface-treated to reflect only light with apredetermined wavelength. For example, if light incident on thereflector is in the predetermined wavelength range, a totally reflectingmaterial (metal material such as Ag and Al, for example) may be providedon the surface of the reflector. If the reflector reflects only light ina specific wavelength range, a material that absorbs or transmits lightin the wavelength range excluding the specific wavelength range is usedas the reflector or a surface is treated to absorb light in thewavelength range excluding the specific wavelength range (irregularity,for example, is provided on the surface). For the semiconductor deviceillustrated in FIG. 5, light emitted by the light emitting layer 110 isreflected by the reflector 21 for the conduction of light to fall on thesemiconductor film 40, varying the threshold voltage of the TFT changeddue to electrical stress.

FIG. 6 illustrates another example of the mechanism for irradiating thesemiconductor with at least a part of light whose wavelength is longerthan the predetermined wavelength. The TFT is fabricated in a top-gateconfiguration. That is to say, the source electrode 50 and the drainelectrode 51 are formed over the substrate 10 and the semiconductor film40 is formed such that the semiconductor film 40 extends over the sourceelectrode 50 and the drain electrode 51. An insulating film (channelprotecting film 60) is formed to cover the semiconductor film 40 and thegate electrode 20 is formed on the semiconductor film 40 situatedbetween the source electrode 50 and the drain electrode 51 and theinsulating film. In the present embodiment, a light transmissive regionis provided in at least a part of the gate electrode 20 and serves asthe foregoing mechanism. The use of a transparent conductor such as ITOor IZO as a material for the gate electrode 20 allows light with shortwavelength to be shut off. For the ITO, for example, if a band gap is3.75 eV, light with a wavelength of 330 nm or shorter can be shut off.

As a material for the insulating substrate 10, there may be used glass,polycarbonate, polyimide, a laminate in which silicon nitride film isstacked thereon and a laminate in which silicon nitride film is stackedon silicon, aluminum or iron alloy.

As a material for the gate electrode 20, it is desirable to use metalssuch as aluminum (Al), silver (Ag), molybdenum (Mo) and titanium (Ti).In addition to the above materials, there may be used a laminate formedof two or more kinds of metals such as titanium and aluminum ormulti-element alloy.

As a material for the gate insulating film 30, there may be used aninsulating film such as a silicon oxide film, a silicon nitride film anda silicon oxide and nitride film and a laminate film thereof.

As a material for the light shielding film 70, it is desirable to use amaterial capable of sufficiently shielding light emitted by the lightemitting element, such as molybdenum (Mo), titanium (Ti) and the like.In addition to the above materials, there may be used a laminate formedof two or more kinds of the materials or multi-element alloy.

As a material for the semiconductor film 40, it is desirable to use asemiconductor with a surface density of in-gap level of 10¹³ cm⁻² eV⁻¹or less because of reducing the influence of excitation of an electron(or a hole) by irradiating the semiconductor film with light whosewavelength is sufficiently longer than the absorption edge wavelength.It is further desirable that the band gap of the semiconductor is 2.7 eVor higher to make the absorption edge wavelength shorter than theemission spectrum of the light emitting element. The reason is that theenergy of “blue” (short in wavelength and its center wavelength is 460nm) largest in energy is 2.7 eV calculated from E=hv=Hc/λ in the case ofthe emission spectrum of the light emitting element forming the lightemitting display element. For this reason, the increase of band gap ofthe semiconductor to 2.7 eV or higher enables suppressing the change inthe S value of the semiconductor (the inverse number of inclination of aLog (Ids)−Vgs curve in the vicinity of Von) and saturation mobility. Asthe semiconductor satisfying the above conditions, there has been knownan oxide semiconductor including at least any of In, Ga, Zn and Sn.Among them, amorphous In—Ga—Zn—O (IGZO) and amorphous In—Zn—O areapplicable to the present invention.

As materials for the source electrode 50 and the drain electrode 51,there can be used titanium (Ti), molybdenum (Mo) and ITO which can bebrought into ohmic contact with the semiconductor layer. There may beused a laminate formed of two or more kinds of materials, ormulti-element alloy.

As a material for the channel protecting film 60, there may be used aninsulating film such as a silicon oxide film, a silicon nitride film anda silicon oxide and nitride film. A laminate formed of two or more kindsof materials may also be used.

A transparent conductor such as ITO, IZO or the like may be used as amaterial for the anode electrode 90.

As a material for the hole transport layer 100, α-NPD, PEDOT or the likemay be used.

As a material for light emitting layer 110, an appropriate material isselected from among organic EL light emitting materials based onemission spectrum.

As a material for the electron transport layer 120, Alq3, PBD or thelike may be used.

As a material for the cathode electrode 130, aluminum (Al), silver (Ag)or the like may be used. There may also be used a laminate formed of twoor more kinds of the materials or multi-element alloy.

EXAMPLES

The examples of the present invention are described below, but thepresent invention is not limited to the following examples.

First Example

In the present example, the following TFT was fabricated to examine thedependency of the change in the threshold voltage on wavelength forestimating the effect of light irradiation on the change in thethreshold voltage.

A TFT to which the present invention is applicable was fabricated in thefollowing steps. FIG. 2 is a cross section thereof.

An n⁺-silicon wafer (height 20 mm×width 20 mm×depth 0.525 mm) with asilicon thermal oxidation film (thickness of 100 nm) was washed to beused as a substrate. An amorphous IGZO being a semiconductor wasdeposited on the substrate by RF magnetron sputtering (deposition gas ofO² (5% by volume)+Ar, a deposition pressure of 0.5 Pa, an applied powerof 200 W and a film thickness of 20 nm). The temperature of thesubstrate is not particularly controlled during the sputteringdeposition. The amorphous IGZO was patterned to a predetermined size byetching to form a channel layer. The entire channel layer was thenheated at 300° C. for 20 minutes under an atmospheric condition. Aphotoresist film was formed and patterned thereon and then titanium andgold were deposited to a depth of 100 nm in total by electron beamevaporation and the resist film was lifted off to form the source anddrain electrodes.

The above steps provide a TFT 200 including a conducting part of thesubstrate as a gate electrode 212, a thermal oxidation film as a gateinsulating film 211, an amorphous IGZO as a channel layer 230, a sourceelectrode 221 and a drain electrode 222. A channel width W is 80 μm anda channel length L is 10 μm. The measurement of the transfercharacteristic √Ids−Vgs characteristic, where Ids is a drain-sourcecurrent and Vgs is a gate-source voltage) of the TFT at a drain-sourcevoltage Vds of +20 V exhibits an n-channel characteristic. The thresholdvoltage (Vth) and the saturation mobility (μsat) determined by thelinear approximation of the √Ids−Vgs characteristic are 4.8 V and 12.9cm²·V⁻¹·s⁻¹ respectively. The S value is 0.6 V·dec⁻¹.

There is examined below the dependency of light irradiation onwavelength in the TFT fabricated in the above manner. The channel of theTFT 200 was irradiated with monochromatic light obtained by leadinglight from a xenon lamp to a diffraction grating spectroscope. Anoptical slit width of the spectroscope is 24 nm. The density of aneutral density (ND) filter put into an optical path is adjusted so thatthe intensity of irradiation is 0.2 mW·cm⁻² for each wavelength.

The TFT was irradiated with monochromatic light having a wavelength of600 nm for 100 seconds and then the transfer characteristic was measuredat a Vds of +0.5 V with the TFT irradiated with the light. Similarly,the TFT was irradiated with monochromatic light having a wavelength of590 nm for 100 seconds and then the transfer characteristic was measuredwith the TFT irradiated with the light. Similarly, measurement wasconducted while wavelength was being scanned by decrements of 10 nm towavelength of 300 nm. The measurements are illustrated in FIG. 3. Forthe sake of simplicity of the figure, the transfer curves are drawn indecrements of 50 nm, with the irradiation light wavelength reduced from600 nm to 550 nm, 500 nm, and so on. The transfer curves monotonouslymove to the negative direction of Vgs without changing the shape of thetransfer curve as the wavelength of the irradiation light is shortened.Furthermore, the S value is increased and the shape of the transfercurve is changed on the side of the wavelength shorter than theabsorption edge wavelength of the semiconductor. Thereby, it is obviousthat irradiation with light having a wavelength longer than anabsorption wavelength of 390 nm of the amorphous IGZO allows shiftingthe threshold voltage to the negative side without changing the shape ofthe transfer curve.

Consequently, in the light emitting display apparatus of the presentexample, the light emitting layer irradiating the semiconductor filmwith light having a wavelength longer than the absorption wavelength ofthe semiconductor through the light transmissive region allows shiftingthe threshold voltage shifted to the positive side caused by electricalstress to the negative side.

Second Example

In the present example, the TFT similar to that in the first example wasfabricated to examine whether light irradiation under various conditionscan compensate or suppress the change in the threshold voltage caused byelectrical stress.

Four TFTs similar to those in the first example were fabricated tomeasure the transfer characteristic at a Vds of +20 V at a dark place.Vds of +0.1 V and Vgs of +20 V as electrical stress were applied to theTFTs for 1800 seconds. The TFTs were irradiated with monochromatic lightfor 1800 seconds under the following conditions different according tothe TFTs:

(4-1) No light irradiation(4-2) 400 nm and 0.02 mW/cm²(4-3) 400 nm and 0.2 mW/cm²(4-4) 600 nm and 0.2 mW/cm².

After that, the light irradiation was stopped and then the transfercharacteristic of the TFTs was measured again at a Vds of +20 V at adark place.

There were determined Vth (threshold voltage), Von (rise voltage, Vgs atwhich Ids exceeds 10⁻¹⁰ A), μsat (saturation mobility) and the S value(the inverse number of inclination of a Log (Ids)−Vgs curve in thevicinity of Von) from each transfer characteristic measured before andafter the application of the electrical stress. FIG. 4 illustrateschange in ΔVth(V) and ΔVon (V) of Vth and Von caused by stress. On theother hand, the saturation mobility μsat and the S value before andafter the application of the electrical stress are little changed withrespect to the initial value, i.e., less than 2% and 6% respectively ineach case and the transfer curves are shifted in parallel with the shapeof the curve maintained. Thus, the threshold voltage of the TFT could bechanged.

Like the above condition (4-2), the irradiation of the TFT causingchange in the threshold voltage due to electrical stress with light doesnot cause change in the threshold voltage, thereby allowing thecompensation of change in the threshold voltage.

Like the above condition (4-4), the irradiation of the TFT causingchange in the threshold voltage due to electrical stress with lighthaving a wavelength of 600 nm makes change in the threshold voltagesmaller than the TFT which is not irradiated with light, therebyallowing the suppression of change in the threshold voltage.

In all the above examples, the characteristics such as charge mobility,the S value and the like excluding the threshold voltage of thesemiconductor element can be maintained equivalently to thecharacteristics obtained before the application of the electrical stressand irradiation with light.

Consequently, in the light emitting display apparatus of the presentexample, it is enabled to control the threshold voltage of the TFT byappropriately selecting through the light transmissive region thewavelength and the intensity of light which is emitted from the lightemitting layer and has a wavelength longer than the absorption edgewavelength of the semiconductor and by irradiating the semiconductorfilm with the light.

Third Example

In the present example, there is fabricated the light emitting displayapparatus being an embodiment of the present invention illustrated inFIG. 5.

The gate electrode 20 and aluminum alloy as the light guiding reflector21 are formed on the glass substrate 10 to a thickness of 100 nm with aDC magnetron sputtering apparatus and processed in a photolithographyprocess and a wet-etching process. The gate electrode 20 and the lightguiding reflector 21 may be connected together or formed in differentlayers. Then, silicon oxide as the gate insulating film 30 is formed toa thickness of 200 nm with an RF magnetron sputtering apparatus (aninter-electrode distance of 110 mm, a power RF of 500 W, Ar of 100 sccm,a pressure of 0.2 Pa and a discharge time of 6 minutes). The amorphousIGZO semiconductor film 40 is formed on the gate insulating film 30 to athickness of 30 nm with the DC magnetron sputtering apparatus (aninter-electrode distance of 110 mm, a power DC of 300 W, O₂/Ar=2/98sccm, a pressure of 0.2 Pa and a discharge time of 35 minutes) and thenprocessed in the photolithography process and the wet-etching process(1N of dil. HCl at 23° C.). Molybdenum as the source electrode 50 andthe drain electrode 51 is formed on the semiconductor film 40 to athickness of 100 nm with the DC magnetron sputtering apparatus andprocessed to a desired shape in the photolithography process and thedry-etching process. Silicon oxide as the channel protecting film 60 isformed thereon to a thickness of 200 nm with the RF magnetron sputteringapparatus (an inter-electrode distance of 110 mm, a power RF of 300 W,O₂/Ar=0/180 sccm, a pressure of 0.2 Pa and a time of 25 minutes),thereby providing the TFT. Molybdenum as the light shielding film 70 isformed to cover the semiconductor film to a thickness of 100 nm with theDC magnetron sputtering apparatus and processed in the photolithographyprocess and the wet-etching process.

Silicon nitride as the protective film 80 is formed to a thickness of200 nm with the CVD apparatus. The contact hole 81 is formed by thephotolithography process and the dry-etching process.

ITO as the anode electrode 90 is formed to a thickness of 150 nm withthe DC magnetron sputtering apparatus and processed in thephotolithography process and the wet-etching process. Thereafter, thehole transport layer 100, the light emitting layer 110 and the electrontransport layer 120 are formed as a light emitting part and aluminum wasformed as the cathode electrode 130.

Finally, the desiccant 140 is sealed in a sealing can 150.

The structure in which emitted light is reflected by the light guidingreflector 21 and incident on the amorphous IGZO of the semiconductorfilm 40 allows suppressing change in the threshold voltage due to theelectrical stress.

Fourth Example

In the present example, there is fabricated the light emitting displayapparatus being an embodiment of the present invention illustrated inFIG. 6.

Silicon oxide as an underlying film 11 is formed on the glass substrate10 to a thickness of 200 nm with the RF magnetron sputtering apparatus(an inter-electrode distance of 110 mm, a power RF of 500 W, Ar of 100sccm, a pressure of 0.2 Pa and a discharge time of 6 minutes). Then,molybdenum as the source electrode 50 and the drain electrode 51 isformed to a thickness of 100 nm with the DC magnetron sputteringapparatus and processed in the photolithography process and thedry-etching process. The amorphous IGZO semiconductor film 40 is formedto a thickness of 30 nm with the DC magnetron sputtering apparatus (aninter-electrode distance of 110 mm, a power DC of 300 W, O₂/Ar=2/98sccm, a pressure of 0.2 Pa and a discharge time of 35 seconds) and thenprocessed in the photolithography process and the wet-etching process.Silicon oxide as an insulating film (the channel protecting film 60) isformed to a thickness of 200 nm with the RF magnetron sputteringapparatus (an inter-electrode distance of 110 mm, a power RF of 300 W,O₂/Ar=20/180 sccm, a pressure of 0.2 Pa and a time of 25 minutes). TheITO as the gate electrode 20 is formed to a thickness of 30 nm with theDC magnetron sputtering apparatus and processed in the photolithographyprocess and the wet-etching process. Molybdenum (Mo) or aluminum (Al)may be stacked to a gate wiring part to reduce its resistance. However,a part of the gate electrode on the channel is formed of a transparentelectrode of ITO to conduct emitted light to the channel part of theTFT. Silicon nitride as the protective film 80 is formed to a thicknessof 20 nm with the CVD apparatus. The contact hole 81 is formed by thephotolithography process and the dry-etching process.

As is the case with the third example, ITO as the anode electrode 90 isformed to a thickness of 150 nm with the DC magnetron sputteringapparatus and processed in the photolithography process and thewet-etching process. Thereafter, the hole transport layer 100, the lightemitting layer 110 and the electron transport layer 120 are formed as alight emitting part and aluminum was formed as the cathode electrode130.

Finally, the desiccant 140 is sealed in a sealing can 150.

The structure in which emitted light is transmitted through thetransparent gate electrode 20 and incident on the amorphous IGZO of thesemiconductor film 40 allows compensating change in the thresholdvoltage due to the electrical stress.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A display comprising: a substrate; a transistorcomprising a gate electrode, a semiconductor layer which includes In,Zn, Ga and O, a source electrode and a drain electrode; a light emittingelement, the light emitting element comprising an anode electrode, acathode electrode and a layer including a light emitting material; alight shielding layer provided between the semiconductor layer and thelight emitting element; and a reflector provided closer than thesemiconductor layer to the substrate.
 2. The display according to claim1, wherein the reflector comprises a metal.
 3. The display according toclaim 2, wherein the gate electrode is provided between thesemiconductor layer and the substrate and the reflector and the gateelectrode form the same layer.
 4. The display according to claim 3, thereflector is connected to the gate electrode.
 5. The display accordingto claim 3, wherein the reflector reflects at least a part of lighthaving a wavelength longer than 390 nm.
 6. The display according toclaim 5, wherein the layer including a light emitting material includesan organic light emitting material.
 7. The display according to claim 6,wherein the light shielding layer shields at least a part of lighthaving a wavelength shorter than 390 nm.
 8. The display according toclaim 7, wherein the light shielding layer is provided at such aposition as to overlap the semiconductor layer when viewed in thedirection that is normal to the substrate.